If using a relay, the switched live (i.e. black wire) would connect to the relay (pin 86) and would need an earth (pin 85). The output from the relay (pin 87) would connect to the coil and the supply to pin 30, this should be protected as close to the battery as possible.

Switched is as the name suggests and simply means the supply has a switch (in this case it's the ignition switch) opposed to being 'hot' i.e. permanently live.

Personally I think it is OTT.

Martin